The Mineralogy of K-Richterite-Bearing Lamproites

American Mineralogist, Volume 71, pages 17-37, 1986

The mineralogy of K-richterite-bearinglamproites

CnnrsutNe WacNrn eNo DeNrrr-r,B Vu-oB Laboratoire de P4trologie Min4ralogique (U.A. 0736 du CNRS) Universit€ Pierre et Marie Curie (Paris 6) 4, Place Jussieu,75230 Paris Cedex 5. France

Abshact The mineralogy and chemistry of eleven phlogopite-richterite-bearinglamproites has beenstudied. It has beenfound that this mineral assemblage(also found in metasomatically altered ultrabasic xenoliths) is typical of peralkaline lamproites. These lavas are typically potassium- and magnesium-rich,with a positive correlation betweenthese two elements, and consequentlybetween peralkalinity and magnesium content. Titanium contents are variable, but may reach 7o/oTiOr. The peralkaline character was acquired before crystallization, all minerals,including the first magmaticphases, having extremelylow Al contents. Loss of alkalis, after partial or complete solidification, can be demonstratedin some specimens. Typical associationsinclude besides phlogopite and richterite, Cr-rich Al-poor spinels,olivine, diopside, Ti-rich oxides (ilmenite, pseudobrookite,priderite). The peralkaline characteris emphasizedby the presenceof roedderite-like phasesin two specimens. An electron microprobe study of lamproite minerals shows a general tetrahedral deficiency in most Al-bearing silicates, the sum Si + Al being systematicallylower than its theoretical value. Most elementsare regularly partitioned betweenco-crystallizing phases: e.9., Fe, Mg and Ti between richterite and phlogopite; Na and K between feldspar and richterite; tetrahedral deficiency between phlogopite and richterite. These observationslead to the conclusion that the peralkaline character of these lamproites imposes constraints on the mineral compositions. However, the mineral compositions are not affectedby the whole-rock silica saturation. Xenocrystic material has been identified and is abundant in lamproites. Isolated relic crystals correspond to most major phases,except for richterite, that crystallize from the liquid, i.e., olivine, clinopyroxene, mica, ilmenite, pseudobrookiteand apatite. A comparison can be made betweenmajor authigenicphases from lamproites and equiv- alent phasesfrom associationsinterpreted, in ultrabasic nodules, as metasomatic assem- blages and presumed to have formed in the mantle under high pressures.Most major element partitioning trends are not affected by pressurebut Ti solubility in silicates is considerably reduced by increasing pressure. The origin of lamproitic liquids cannot be linked to basaltic magmas;basalts are indeed absent from lamproitic provinces. The observed bulk composition of lamproites could result from melting of richterite + phlogopite-bearingultrabasic associations in the mantle. Calculations indicate that for all specimensconsidered in the present study the initial proportions could be richterite 30-500/oand phlogopite 56-680/0.Precipitation of olivine (with or without diopside) could then lead to the observedlamproitic lava compositions.

volcanic or subvolcanic rocks with a unique paragenesis Introduction that includes the rare minerals, K-richterite and priderite. The term lamproite was coined by Niggli (1923, p. 105) According to Scott Smith and Skinner (1984), current for rocks whose compositions were extreme with respect research shows that "lamproites are characterized by Ti- to their potassium and magnesium(hrgh) and aluminum rich silicatesand oxides, while the absenceof plagioclase (low) contents.The term has beenused since, to designate and significant amounts of melilite separatesthem from rocks with compositionssimilar to thoseof lamprophyres, other potassium-rich alkaline rocks." Lamproite is used but whose field relations clearly indicate a volcanic situ- in the present work in Rock's general definition but, as ation (Velde, 1969, 1975). pointed out by Scott Smith and Skinner (1984), the pres- Recentdefinitions take into accountmineralogical com- ence of Tirich silicates and oxides definitely appearsto positions. The term is thus restricted by Rock (1984) to characterue this group of lavas. 0003404x/86/0r024017$02.00 r7 18 WAGNER AND VELDE: K.RICHTERITE-BEARING I.IIMPROITES

Table l. List ofthe samplesstudied, geographicallocalization, age,mineral assemblagesand referencesto previous studies

'l::.ti* Localiri es Rock rype Ase uineralogical Assenblag€ References numbet

SPAIN 01+Cpx+PhI+Richt+Kspar+Cr+I1o Lewis ( I882) Osann ( 1906) Jerenine and I'allot (1929) ( cancarix, Albacete 74Al Cancalile 5.7 to 7.6 m.y. Ac+Ap+r'Roed'r+Ru+Cc hernandez ?acheco 1935) x-ol ? x-cr ? San Miguel de Ia Canala et (19s2) (1965) 2 Calesparra. Murcia 72Ai BeIIon et ar.(1981) Ap+GIass+X-01 ? Iuster and castesi Be1lon (i976;1981) Fuster et aI. ' (1967). 3 Juni1la, Murcia llA8 JumiIIite lc+Ac+Ap+CIass NODei eE af. (lv6l, Borley ( 1967) (1969) Barqueros, Murcia 73A8 lortunite MonEenat et al. velde (l975) X+Ph1+x-AL-Sp+X-Psb+X-1 lm+x-Ru Ruiz and Badiola (198o) Nixon et al. (1982)

UNITED STATES Smoky Butte, MonEana 788 Leploice 27 n.y. o1 (a1r. ) +cpx+Ph1+Richt Matson ( l960) hrvin et al.(198o) +Ksper+Ana1+Ap+GIass verde (1975) +Psb+Prid+cr ( Sbiprock dyke, 586 MineEte 27-30 @.y. 01 (a1t) +Cpx+Ph1+Richt- Williaos 1936) Nev Mexico Naeser (1971) A!fv+Kspar+Ap+Glas s+ Nicholls (1969) Amstrong (1969) Ilm+!'lr+Ac velde (1969) Roden(1981) Moon Canyon, ljtah MC77 Lanproite 36-40 E.y. O1(alE) +Cpx+Ph1+Richl+ Kspar+Ap+G1ass+I1m+ Critlenden and Kistler (1966) Psb+"Roed"+c!+x-Ph1 Best et al. (1968)

FRANCE sisco, corsica 6 1A3 15.4-13.5.n.y. 01(altlcpx+Ph1+Richt- velde (1967) (1968) sisco, corsica 8Al2 Feraud et aL.(1977) Arfv+(sPar+I1m+Prid+Cr verde CiveE!a et al. (1978) +Ru+AP+Sph+Cc Bel1on (1981)

AUSTRA]-IA Wadeand Prider (1939) ( Mount Norlh, s0136 wolgidite 17-22 n.y. O1(al E)+Cpx+Ph1+Richt+ Carmichael 1967) 1m+Prid+Ap+G1ass Kaplan et al. (1961) tlest Kioberley (1982) Lc+I Jaques et al. Mitchell (1981) Jaques et al. (1984)

ITAI,Y (1967) orciatico, Pisa selagite 4-l E.y. O1+Cpx+Ph1+Kspar+IIm Barberi and Innocenti borsl et al. t lvo/, +Richt+Cr+Ap stefanini ( 1934)

(diopside) ; Abbreviations : Ac, amite ; Af-Sp, aiuninous spjne] ,. Anaf, anaTcite ; Arfvt arfveilsonite ; Cc, cafcite ; Cpx, cfinopgroxene aftereal ofivine ; Ct, chronite; Itnt ifnenite ; Kspar, poxassiun fefdspat , Lc, leucite; Mt, Mgnetite ; of, oTivine ; Of(alx), phase Ru, rutife; phf, phTogopite ; psb, pseudobrookixe ; Ptid, ptiderite ; Richt,richterite; "Roed", roedderite-fike ; xenoctgst. Sph, sphene. -X jndjcates that tle species whose abbreviated nane folfows is ptesent, but intetpteted as a

The phlogopite-K-richterite association is also record- Counting time : 30 s; acceleratingvoltage : 15 kV; cur- ed from nodules found in kimberlites, the uanro suite as rent : 30 nA for oxides; 5 nA for feldspars. defined by Dawson and Smith (1977). The mineralogical phasespres- associationsas well as the composition of the Chemical compositionand peralkaline ent is similar in the nodules and in the lamproites. It character of the lamProites seemedwarranted to examine the compositions of these phasesand their crystallizationrelationships in lamproites The eleven specimensstudied in this paper come from and consider more closely the similarities and differences most of the classicallocalities. Their agesvary from 40 between the constituent minerals of lamproites and the to 4.1 m.y.; they usually occur as pipes, dikes or necks metasomatic assemblagesfrom mantle rocks that could but flows are also found. Table I gives the list of all sam- be the sourceof lamproites. ples studied and Table 2 the correspondingbulk chemical Experimental bulk rock analyseswere perfbrmed using compositions. a Philips PW 1400 spectrometer.Ferrous iron was deter- Lamproites are magnesium-rich: their CIPW nonns mined using a method outlined by Peck (1964) and HrO* show 200/onormative enstatite(or diopside) with or with- by a modified Penfield method. out forsterite.They are potassium-rich,and analysesshow Electron microprobe analyseswere carried out on an a positive correlation betweenpotassium and magnesium, MS-46 cAMEcAinstrument with natural or synthetic min- a significant difference with usual trends in magmatic se- erals as standards for olivines, micas, amphiboles and ries. No correlation is observedbetween alkalis and iron clinopyroxenes.Counting time : 30 s; acceleratingvolt- content. In the specimensstudied, KrO varies between 7 age: 15 kV; current : 30 nA (20 nA for K and Na in and l2o/o(except the Jumilla specimenwhere the present micas and amphiboles).Other mineral compositionswere KrO content is only 3.70lo),and is largelysuperior to NarO. determined u.ith a cAMEBAxautomated electron micro- Titanium contents are variable, and can reach 7oloTiOr. probe usingeither oxidesor natural minerals as standards. This is particularly striking when considered in connec- I4/AGNER AND VELDE : K-RICHTERITE-BEARING I,,,IMPROITES t9

Table 2. Chemical composition of the samplesstudied. All analysesare new but for Nos. 6, 8, lO

t2 34 567 8 9 l0 lr 74At 72A7 I lA8 73A8 7B8 yrc72 586 sol36 6lA3 8Al2 60A7

sio2 55.41 56. 6I 47.31 58,77 5l,41 55.73 53.70 45.82 57.46 56.23 57 .8 I A1203 8.83 7.96 6.52 I I .34 8.36 1O,72 I 1.06 6.86 10.88 12.06 10.94 F"203 l.l7 2.12 3.83 I.3t 3.O2 3.73 3.57 6.07 1.46 l 9 I 3.55 FeO 3.40 3.13 2 .88 3.49 2.31 0 .95 3.08 1.98 2.54 2.9t r.44 Mgo I 3.59 12.45 t7.t6 9.22 8.05 6.96 7.86 10.90 7.24 6.90 8.26 cao 3.91 2.97 8.82 2.7I 4.7t 3.85 7.38 4.70 2.96 3.48 4.43 Na20 l.l3 0.75 1.88 I .08 1.25 | .2t 2.31 0.84 t.14 1.03 1.09 K2O 8'63 9.21 3.7t 8.46 7.87 10,49 6.64 8.82 10.75 10.00 7.94 MnO 0.08 0.08 0,t2 0.10 0.06 0,08 0. l0 0. I0 0,05 0.o7 0.07 TiO2 1.41 l.6l | .32 I .35 5.46 2,82 l.8l 7.34 2.19 1.14 t.37 PzOs t.35 1.23 2.OO O,19 2.22 1.13 0.91 I .83 0.14 0 .79 0.72 BaO 0.35 t.27 co2 0.08 0.41 H20+ 0,59 1.86 3.77 0,96 3,58 l.14 1.53 o.75 1.70 1.56 l.t8 H2O- O.23 0.65 t.3l 0.31 t,74 0.89 0.62 2.40 0.72 1.58 1.06 F 0.36 0,41 0.32 0.30 0.46 0.16 0,38 0.35 0.33 Clppm 226 321 t74 87 78 45 319 74

Total 100.I 5 l0l .04 100.95 100.19 100.50 100,05 r00.73 99.76 100.21 tOO,42 100,19 0=F 0.15 0.17 0.13 0.13 0. 19 0,07 0. 16 0. 15 0. 14

Total 100.00 100.87 I 00.82 I 00.06 100.31 |00.66 100.05 100.27 100.05

Na+K l.4l 1.09 0.96 A1 | .26 1.24 0.99 1.59 t.24 1.04 0.95

a 2.90 2.27 3. 14 2.33 4.61 Or 48.15 43.37 21.90 50.04 45.65 58,53 39.25 37.25 59.32 59,10 46.98 Ab 12.42 9 .t2 l7 .34 6.36 9.22 AN 1.06 0.14 1.45 Ac 3.37 5.57 2.68 8.73 9.O2 6.47 4.20 2.08 Ne o.23 1.19 Ns 0.16 l.l3 Ks 0.80 3.08 o .26 0,96 4.t6 l l8 DA 8 .65 5 .29 24.O7 5.75 4.34 23,80 7.76 7,92 12.33 En 21.20 28.87 20.77 20.13 15.32 27.20 14.69 f0.55 t4.94 Fs 2.44 2.85 3.92 o.92 I .60 Fo 6.30 22,35 6.03 2.38 Fa 0.80 0.53 0.40 MI 0 ,28 4 .20 5.0I t.73 0.90 HeE 0.61 0. I I 4.00 2.93 IIE 2.68 3.05 2.51 2.57 5.00 2.18 3.44 4.4t 4.t6 2, l7 2.60 Tn 6.39 3,85 1.37 Pf 0.18 6.12 Ru o.22 0.88 AP 3.19 2.92 4.70 1.88 5.24 2.73 2.15 4.03 1.75 t,73 l.7l Cc 0.20 0.93

Analyeis 6, Best et al., 1968; Analysis 8, Wadeand prider, 1940; Analysis 10, Velde, 1967.

tion with the low iron content of these rocks in general gument is the fact that lamproites often occur with glassy (4.0 to 6.10/oFeO* FerO, and 8goin specimenSOl36). textures,frequent among the Spanishlamproites, present The specimensexamined are either definitely peralka- in Smoky Butte and the Leucite Hills, and recently de- line or close to peralkalinity. This character is demon- scribed in Australia (Prider, 1982). The second line of strated by the presenceof normative acmite in the CIPW evidenceis that the spinelsfound in olivines ofthe Spanish norrn, accompaniedby sodium ald/or potassium meta- lamproites, Sisco, Moon Canyon, the selagitesand the silicate, the maximum content ofnormative anorthite being Smoky Butte lamproite are uncommonly chrome-rich (51 1.45% (Table 2). Fluorine (between 0.2 and 0.470lo)is to 6506CrrOr) but always alumina-poor (0.23o/oto 4o/o positively correlatedwith potassiumcontent following the AlrO3) fiable 3). In comparing data on various olivine- relationshipdiscovered by Aoki et al. (1981). bearinglavas, it appearsthat the AlrO, content of Cr-rich Two lines of evidence indicate the primary origin of the spinelsis related to the composition of the rocks in which peralkaline character of the lamproitic rnagma. One ar- they are found. Using, for example,analyses published by 20 WAGNE R AN D VELD E : K. RI CHTE RI TE -B E AR I NG I.'/IMPRO ITE S

Tabte 3. Representative electron microprobe analysesof chrome spinels found as inclusions in the olivines. Fe3+calculated assuming 3 cations and 4 oxygens

r234567891011 7 4A1 7 4Ar 12A7 72A7 11A8 11A8 73A8 6818 8Ar2 60A7 60A7

A1^O^ O.23 0.15 3,O4 t.12 2.OO 1.16 1.10 0.71 4.16 3.56 7.87 Cr^O^ 51.41 62.64 65.34 61.43 55.78 51.48 31.58 42.78 63.OO ss.64 36.22 FeO 37.05 26.40 20.33 29.99 29.34 34.91 46,72 32.84 15.31 30.17 47.95 MgO 4.42 8.OO 10.41 4,72 9. 80 7.43 5.24 9.54 13.80 5.77 3.30 MnO 0.84 O,82 O.69 O.90 o.79 0.47 o,55 0.61 o, 48 0. 80 0.86 Tio^ 4.52 1.16 1.23 t.63 1,03 0.79 r0.90 9.50 2.r4 7.L2 5,70 ZnO od nd nd nd nd nd nd 0.32 O.2O nd nd

TotaI 98.47 99.17 101.04 1OO.39 98.74 96.30 96.O9 96.30 99,09 97.06 9s.90

Fe^O^ 9.77 7,78 3.22 4.54 73.32 16.39 15.79 9.59 2.97 7.13 19,2'7 FeO 28.26 t9.94 L7.43 25.90 17,35 20.23 32.51 24,22 12.64 23.21 30.61

Al O.O10 0.006 0.120 0.072 0,081 0.049 o.o48 0.o30 0.163 0. 151 0.O82 Fe3+ 0.267 o.19o 0.081 O,L2l 0.345 0.444 o.436 0.257 0,074 0, 209 0.538 Cr 1,476 I.7 42 I.736 I.72O 1.520 r.464 o.916 L.205 1.656 1.580 7.062 Fez+ 0.858 O.587 0.49O O.767 o.500 0.609 0.997 0.12r 0.3s1 0.697 0.949 Mg 0.239 O.42o 0,522 0.249 0.504 0.399 o.286 0.506 o.684 0.309 0.182 Un 0.026 O.O24 O,O2O O.o27 0.o23 0,014 0.o17 0.o18 0.014 0.o24 0.027 Ti 0.723 0.031 0.031 0.043 o.o27 0.021 0.301 0.254 0.053 0.030 0.159 Zn o.oo8 o. oo5

FeOo : Total iron as Feo nd : noL sought for.

Eissen(1982) on MORB basaltsand Barbot (1983) on by Yelde and Yoder (pers. com.). The peralkaline char- spinelsfrom alka[ basalts,it can be seenthat for a given acterof the lamproites could, in someinstances, have been Cr content, spinels from tholeitic basalts are richer in more pronouncedthan presentlyevidenced by their bulk AlrO, than spinelsfound in alkali basalts.Within the field composition. Specimen I lA8, from Jumilla, contains of alkaline rocks, spinels are richer in aluminum in alu- apatite phenocrystswith frequent glassinclusions. One of mina saturated melilite-bearing compositions than they these(0.06 x 0.03 mm) containsbesides glass, a euhedral are in peralkaline compositions, the two fields showing crystal of olivine and a small mica blade, both phases no overlap (Velde and Yoder, 1983; unpublished data). appearingas phenocrystsin the rock. This glass(Table 4) In the lamproites the Cr-rich spinelscan be consideredas is considerably richer in alkalis than the bulk rock and the liquidus phase.From their rather unique composition, the (Na + K)/Al of the glassinclusion is 1.72 as opposed they definitely belong to the peralkaline field as defined to 1.09 for the bulk rock composition. kast squarescal- culations made to estimatewhether the glasscomposition could be derived from the bulk composition of the rock, into accountthe presenceofthe olivine and biotite Table4. Electronmicroprobe analyses ofthe gJass(1 : average taking if it of 3 determinations)and olivine (2) includedin an apatitecrystal crystals, show that a reasonablefit is obtained only from specimenI lA8 is assumed that the bulk composition has lost alkalis (mostly potassium)after inclusion of the Slassin the apatite. From the above one can consider that the lamproite sioz 55.00 4o.oo liquids that produced phogopite and K-richterite assem- o1203 12.00 blageshad primary peralkaline compositions. This char- 11.00 Feoo 6.00 acter was acquired before the first liquidus phase (Cr- ugo 1.30 50.00 spinel) crystallized.In at leastone specimen(l lA8) it can CaO 1.60 0.20 that the composition was altered after Na20 5.oO be demonstrated (see K2O 12,OO the crystallization ofthe feldspar below) and originally

MnO O.2O had a stronger peralkaline characteristic. Tio2 2.60 Finally, the silica saturation is not a factor critical to under consideration since Total 95.50 1o1.40 the mineralogical association lamproite compositions can vary from undersaturatedwith

feu" = loEar lron as reu respectto silica (with modal felspathoid)to oversaturated (with modal qtartz). WAGNERAND VELDE: K-RICHTERITE-BEARING LAMPROITES 2I

Table 8. Representative electron microprobe analyses of feldspars from the lamproites studied. Total iron : FerO,

t2 t4) 678 910L7 12 13 74A7 72A7 11A8 11A8 7348 7B8 5B6 586 MC77 6143 61A3 60A7 6047

sio2 63,90 63.9r 6t.28 63.11 63.81 63.61 63.22 65.O2 63.23 64.24 64.63 64,99 64.65 Al2o3 r7.46 17.72 12.85 t4.49 18.59 L5.76 19.00 18.41 15.86 77.29 18.24 L4.57 L8.52 Fe2O3 L.I2 7.26 4.95 3.L7 0.31 1.93 0.62 0.62 2.97 1.L4 0.20 o.51 0.78 l'{go o. 02 O.03 o.10 0. 20 o.08 CaO 0.11 0.10 Na2o o.44 0.63 o.66 0.32 L.39 o. 5s 3.25 3. 53 o.32 0.42 0.56 2.25 2.29 K2O 16.15 75'75 16.38 16.20 14.50 15.83 10.98 r.52 15.84 76.21 75.97 73.34 12.98 Bao O.25 O.39 0.11 0.o8 0,64 r.21 l.a1 0.50 0.11 0.34 o. 06 0.89 Tio2 o.27 O.29 o.42 0.22 0,16 0.33 0.26 o.29 0.I2 0.07 o.17 0.40

Total 99.61 99.38 96.75 91.79 99.@ 99.22 99.os 99.46 99.03 99. 53 100.o1 99.89 100.51

si 2.946 2.993 3.or2 3,o28 2.969 3.013 2.945 2.ga0 2.994 3.OoO 2.994 2.982 2.966 A1 0.962 0.945 o,745 0. 820 1.020 o.880 1.043 0,995 o.885 0,952 0.996 1. OO4 1. OO2 Fe3+ o.039 0.o44 o,183 0.114 0.011 o.069 0.o22 0.021 0.104 0.040 0.o07 0.018 0.o21 Mg O.OO1 o.oo2 o. oo7 0. o14 o. 006 o.oo5 0.0o5 Na O,O4O O.O57 o.063 0.o30 0.125 o. o51 0.294 0.314 o. o29 0.038 0. o50 o,200 0. 204 K 0.963 0.941 L.O21 0.992 0.861 0.957 0,653 0.674 o.951 0.966 0.944 0.781 0.760 Ba O.OO5 O.OO7 o.oo2 0.002 0.012 o.o23 0.034 o. oo9 0. oo2 0. 006 o.ool 0.016 Ti o.oo9 0.010 0.016 0,oo8 0.006 o.o12 0.009 o.010 0.o04 0.0o2 o.006 0.014 5.oo5 5.0o1 5.050 5.0o8 5.003 s.oo4 4.996 4.991 4.994 5.OO2 4.999 4.992 4.988

Mineralogy contentsfound in olivines from nodules occurringin kimberlites (Nixon and Boyd, 1973; l98l) A general order of crystallization can be deduced from the Scott, and similar also to values recently determined in textural relationshipsof the lamproites studied. In all specimens the Australian lamproites and kimberlites (Jaqueset al., 1984). olivine appears to be the first silicate phase to appear. The Cr- The NiO content of the is inversely rich spinelsare only found as inclusionsin olivine. Diopside and olivines correlated with the fayalite (Forr) phlogopite have probably syncrystallized; amphibole and feld- content. In the selagite,the most ferrous olivine spar have appeared subsequently and are contemporaneous with contains 0.230loNiO. Calcium in the olivines is usually low, particularly an acmitic rim on the clinopyroxenesand in someinstances with in the xenocrysts,but always below 0.200loCaO. There is a positive a deeply red colored edge around the phlogopites. Oxides appear correlation between CaO and fayalite contents of the olivine. to have formed after the diopside and the phlogopitic centers of the micas. The specimenfrom Moon Canyon shows phlogopite The manganesecontents are consistently high and positively surrounding olivine crystals, and richterite rimming the diopside, correlated with the fayalite content; MnO is close to 0.30o/oat thus supporting the order stated. It should also be mentioned Foro. that, when present,feldspar often showsa skeletalhabit. Modal analysesare given in Table 5.t Pyroxene Clinopyroxene(Table 7r) in the lamproites studied falls mostly Olivine in the endiopside field of the pyroxene quadrilateral. Its abun- Olivine is found unaltered only in some Spanish specimensand dance varies from 6 to 22Yoin volume. It most often occurs as the Orciatico selagite.In both types, some crystals (usually an- unzonedphenocrysts which contain around 1oloTiOr. The CrrO, hedral, and large in size) represent xenocrysts with typical kink- content variesbetween 0.1 and 0.3 but, in the Spanishlamproites bands.Phenocrysts are generallyeuhedral in outline, and contain falls in the 0.44.9o/orange. These values are considerablyhigher numerouseuhedral spinel inclusions.Compositions of the xeno- than those commonly found in lavas and are, for the highest crystsare similar to that of the coresof the phenocrysts,in major ones, consistent with percentagesrecorded from diopsides from elements(Foo/o) or trace elements (Ni for example). Composi dunite inclusions (e.g.,Berger, 1981). tions, including xenocrysts(Table 6') vary from 92 to 77o/oFo. In all samples,save the specimen from Shiprock (586), the Nickel contents are consistentlyhigh, vary from 0.10 to 0.700/o tetrahedral site ofthe pyroxene is incompletely filled by Si and NiO, but usually occur between 0.30 and 0.500/0.Such hieh Ni Al; the tetrahedralsite occupancyvaries from 1.94 to 2.00, usu- contents are above the values given for olivine in basalts (between ally being between 1.97 and 1.98 atoms. The site can be consid- 0.10 and 0.30 NiO, Simkin and Smith, 1970; Anderson and ered as completedby Fe3* atoms that are presentwhen the stmc- Wright, 1972). They are comparable to values reported by Reid tural formula is calculated on 4 cations and 6 oxygens. This et al. (1975) in olivine from peridotite xenoliths, close to Ni deficiencyin Si + Al was noted by Carmichael (1967) for the Leucite Hills diopside and is mentioned by Jaqueset d. (1984) I To receivecopies of Tables 5, 6, 7, 14, 15, and 16, order for the Australian lamproites. This situation can be related to Document AM-86-292 frorn the Business Ofrce, Mineralogical the low-alumina content of the liquid from which the pyroxenes loge1V g{Ameic,a, 1625I Street,N.W., Suite 414, Washington, crystallized.Acmite is presentin many samples,as a thin, late D.C. 20006. Pleaseremit $5.00 in advance for the microfiihe. rim around the diopside crystals, or small groundmass grains. 22 WAGNER AND VELDE : K-RICHTERITE-BEARING LAMPROITES

Y + G

o z ".\n I '.:t Y

Fe3+ feldsDar Fig. l. The joint distribution of (Na + K) - Al calculated Y from the bulk rock composition and the Fe3+content offeldspar + (mole%). (specimen G Solid squares:data from this study numbers z are listed in Table l); solid circle: LH9, Carmichael(1967). Open square: Jumilla composition correcled for calculated alkali loss.

In two specimens(Shiprock, 586 and Smoky Butte, 7B8) some of the colorless diopside phenocrysts show a gteen center. In Shiprock the green cores are richer in Al, Fe Na and than the o.5 1.O (1981) pres- diopside zone.Barton and Bergen have reported the Ca ence of green clinopyroxenes with a salitic composition in a kucite Hills wyomingite, and this type of clinopynoxenehas fre- Fig. 2. (a) The distribution of Na + K and Ca in richterites quenfly been found in alkali-rich, potassic rocks (Barton and from specimen7B8. O) The distribution of Na + K and Ca in Bergen,1981; Lloyd, l98l). Thesegreen centers in diopsidesare richterites from specimen586. commonly interpreted as being xenocrysts,coming from the dis- agglegationofclinopyroxenite nodules,and appearto be a ubiq- The feldspars are titanium-rich. Percentagesof TiO, in the uitous feature of potassicvolcanics. lamproite feldsparsanalyzed reach0.45o/o; Best et al. (1968) give 0.500/ofor a Moon Canyon feldspar,values that are considerably Feldspar higher than the 0.07 to 0.080/orecorded by Smith (1974) in his Feldsparis abundant (19 to 480/oin volume) and appearslate treatise. Feldspars from the Sisco minette, which coexist in the in the crystallizationsequence; it is absentfrom the Mount North groundmass with abundant minute sphene needles, show the Australian lamproite which carries leucite and from some of the lowest values (0.07% TiOr). No simple relationship is apparent glassyspecimens. In all but two casesthe feldspar composition between the TiO, content of the feldspars and the TiO, content is closeto that of the potassicend member (Or 95-98). Feldspars of the liquid from which they crystallized. from the Shiprock and Barquerosspecimens are more sodic (64 Barium varies betwen 0.1 and 0.390BaO. but can reach0.620/o to 72, and,87 to 890/oOr respectively)(Table 8). (73A8) and l.3ob (7B8). Two specimensshow largevariations in Iron contents are high, usually varying between I and 20loFerOr, the barium contents of the feldspar: in sample 60A7, BaO varies but reaching 2.5o/oat Moon Canyon and 590 in the jumillite. from 0 to 0.89%, and in sample 586 from 0.0 to 3.22%BaO. Carmichael(1967) reportsvaluesbetween 3 and 40loin the Leucite In both cases there is an inverse correlation between BaO and Hills lamproites and Best et al. (1968) 3.830/oin some of the the sum NarO + KrO. Moon Canyon specimens.According to Smith (1974) the iron Amphibole content offeldspars could be related to a rapid growth rate. Though feldspars in lamproites have crystallized rapidly as exemplified Amphiboles found in peralkaline lamproites belong to the rich- by their common skeletal habit, the iron content cannot be ex- terite group and are characterized by the presenceofa high pro- clusively linked to the growth rate, but can definitely be correlated portion ofpotassium in the A site. They are among the last phases with the peralkalinity of the liquid (Fig. l). The only exception to appearand are found, albeit in small amounts, even in some is the Jumilla feldspar whose abnormal position on the diagram lamproites that do not have a peralkaline composition (e.g.,the is consistentwith the alkali loss already addressedabove. selagite). In this case, their presence indicates that towards the WAGNER AND VELDE: K.RICHTERITE-BEARING LAMPROITES z5

Richt6rite 10 o8 t : a + ^ o ^^ (J os o tAo,^o o

o A Arfvedsonite

100 105 110 Si+Na+K Fig. 3. The distribution of Ca * AlIv and Si + Na + K in richterites from specimen61A3. 15-6 15 8 16.0 end of the crystallization sequenceat least the residual liquids E cations wereperalkaline. Richterites belong to the calcalkalineamphibole Fig. 4. The distribution of Ti and the sum of cations in rich- group and their general formula can be written terites from 74Al (solid triangles) arrd72A7 (open circles). (Na,K)NaCaMg,Fe2*)rSi*Orr(OH)r. The richterites analyzed have at most one Fe2* atom in the C site, except for the amphiboles found in the Shiprock and Sisco specimensthat are richer in iron strating this tetrahedral deficiency. The tetrahedral site must then (varying between MgrFe, and MgrFer). contain another ion which could be Fe3+.When calculatedFe3+ Their composition is usually close to the theoretical richterite is assignedto the tetrahedral site, the structural formula usually composition (e.g.,7B8, Fig.2a), or intermediate (asin Shiprock, becomesacceptable, the tetrahedral site is filled and there is no Fig. 2b) between richterite and arfuedsonite (Table 9). The struc- excessof ions in the A site. In some analyseshowever (e.g.,in tural formulae were computed following the method of Papike Calasparra)the tetrahedral site cannot be filled by Si, Al and Fe3+ et al. (1974) as advocatedby kake (1978). Initially the A site and the presenceof yet another ion should be considered. (Na + K) is overfilled and the tetrahedral site is underfilled (Si + The richterites are Ti-rich: the minimal values found are close At < 8). In Figure 3 the trend shown by the experimental points to 2o/oT7Or,in Siscofor example,but reach990 in Moon Canyon. is parallel to the theoretical richterite-arfredsonite line demon- In amphiboles with high Ti contents (Cancarix, Calasparraand

Table 9. Representativeelectron microprobe analysesof K-richterites from the lamproites studied. Structural formulae calculated on the basis of23 oxYgens

1234 5 6 7 8 9 10 11 12 13 14 15 16 74At 7 4AI 72A7 11A8 11A8 73A8 788 )bo MC77 MC77 61A3 8A12 30136 50136 60A7 sloz 52.49 52.92 5L.79 52.31 53.22 54.40 53.26 51.tO 48.85 5r.12 50.06 51,55 52.O2 52,46 57.24 54.50 AIzO3 O'41 o.55 0.36 1.O1 o.32 0.33 0,38 7,75 r.62 0.51 o,25 0.36 o.40 0.33 o.53 0.93 FeOo 4.51 13.64 6.62 1.99 9.55 7.08 4.22 13.21 17.85 5.53 8,29 76,'78 L2.35 2,94 5.45 8.05 Mgo 18.65 t1.17 77,24 t7.O9 16.70 18,58 18,93 75.O2 12.36 l'7.06 14,64 70.14 76,25 20,55 18.12 18.13 CaO 6.68 4.44 5.19 3.51 4.05 5,84 6.17 3,87 7.99 6.38 4.30 r.2r 6.44 6.58 6.68 8.34 NarO 4.24 4.67 4.15 6.33 6,43 5.01 4.27 6.95 8.26 4,33 4,96 6,66 3.85 3.29 3,64 3.4 K2O 3.64 4.12 3.69 2.a9 2.94 2,51 4,25 1.62 t.52 4.22 3,94 4,34 3.56 5.81 5.55 1.12 MnO o.10 0.13 0.14 0.09 o,22 0.77 o.2t o.12 o. 11 0.04 o.24 0,o4 o.05 0.11 Tio2 5.t4 7.16 5.66 5.42 4.19 3.81 5.10 3.55 3,23 7.44 a.41 6.5t, 2.56 5.04 6.34 r.64

Total 96.76 98.61 96.0O 96,68 91. 54 97.65 97,00 97.25 95.88 96.7r 95.06 97.62 97.67 91,70 97.60 96.42

'1.632 't.577 't si 7,725 7. 588 .711 7,7 47 7.633 1.527 7, 488 7. 432 1.470 7.736 1,651 7.532 1,t+22 7.833 Al 0,069 o.094 0.062 o.t'73 0.o55 o,055 0.065 0.303 0,293 0.087 o.044 0.063 o.069 0.055 o.090 0.157 Fez+ o.544 1.665 0,809 0.969 1.r57 o,843 0, 506 r.627 2.2A8 0,612 1.O35 2.106 L.520 0,353 o.661 0,967 Mg 4.017 2.430 3,159 3.695 3.606 3.943 4.o43 3.299 2.824 3,691 3.265 2,267 3. 565 4,397 3,911 3,884 Ca 1.033 o.694 0.908 o.546 0.629 o.891 0.979 o.611 0.326 0.994 0.688 0.t94 1.016 1,Or2 7,037 L.245 Na 1.185 r,32L 1.347 1.780 1.806 1.383 1.187 1.986 2.4s6 1.221 1.435 1.938 1,099 0,9L6 L,O24 0.948 K 0.669 o.767 0.688 o, 535 0,543 o.456 0.777 o.305 0.297 0,783 0.750 0.830 o.669 r,O16 7.026 0,242 Itn o.012 o.016 0.017 o.011 0.o27 o.021 0.o27 0.015 0.014 0.0o5 0.o30 0.005 o.006 0.o13 Ti 0,558 o.786 0.622 0.591 0,451 o.408 0, 550 o.394 0.372 0.813 0,951 0,738 0.283 0.544 o.690 0,177 lotal 15.7O1 15.485 15,784 15.892 15.980 15.737 L5.161 16.olJ 16.310 15.726 15,652 15.877 15.908 15.890 15.867 15.506

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15.6 15.a 16.0 E cations 7.6 78 80 E cations Fig. 5. The distribution ofTi and the sum ofcations in richterites from MC77 (open squares)and l1A8 (solid squares). Fig. 6. The distribution ofTi and the sum ofcations in phlogopitesfrom 3 specimens.Open squares,586; opencircles, SO I 36; solid stars.8A12. Moon Canyon) the inclusion of titanium createsa vacancyin the structure as can be shown on a diagam showing the variation of Ti vs. the sum of ions (Figs. 4 and 5), an analogoussituation either as cores of complex micas, or have served as nuclei for to that described below in trioctahedral micas. Amphiboles with lamproitic micas crystallization. They may (7B8, 586) or may lower Ti-contents from all other specimens display a negative not (7441, 72A7,7B,8,586, 8Al2) appearunstable, with Ti- correlation between titanium content and the number of Si + Al oxide exsolutions. Surrounding lamproitic micas are higher in ions on the tetrahedral site, but no relationship is found between Ti, Fe and lower in Al than the cores which show TiO, contents Ti content and the sum of cations. around 2ol0,and significantCr2O3 percentages (from 0.30 to 1.0). Some amphiboles are zoned: richterite from the Cancarix and Such high CrrO, contents have been recorded from peridotites Australian specimens show a darker color towards the rims of (e.g.,Boyd and Nixon, 1978; Delaney et al., 1980; Jones et al., the crystals, and this variation corresponds to an increase in 1982) or from phlogopite centers in some Monument Valley titanium and iron and a decrease in magnesium without any minettes (Jonesand Smith, 1983).Typical lamproite micas plot significant variation of the other elements, probably indicating near the phlogopite composition, the Fe/(Fe + Mg) ratio always thesubstitutiontr + Ti + Fe2+:3Mg. below 0.30. They are often zoned concentrically, with an increase The main diference between these amphiboles and richterites of both Ti and Fe and a concommitant decreasein Al from center found in the ulnro suite nodules rests with their TiO, content, to edge. They show a deficit in the tetrahedral site, Si + Al + higher in the lavas than in the high-pressure xenoliths. Cr < 4 atoms. Concerning the substitution in the tetrahedral site, several pos- Mica sibilities have been investigated. The presence of Fe3* on the tetrahedral site ofmicas has long been known. Tetraferriphlog- Trioctahedral micas (representative analysesare listed in Table opite is found in nature (Cross, 1897) and has been synthesized l0) represent an important constituent of the lamproite miner- in the laboratory. Silicon and magnesium can proxy for alumi- alogy, from 15 to 30% in volume. num on the tetrahedralsite (Seifertand Schreyer,197 l;Tateyarna Two kinds of micas are present, some are authigenic crystals et aI., 1974\. whereas others can be interpret€d, with various degrees of cer- Robert (198l) showed(using infrared techniques)the presence tainty, as xenocrysts.In two specimens(7348 and MC77) large of tetrahedral Mg in a Smoky Butte lamproite phlogopite. He independent crystals of phlogopite appear to have been desta- was also able to demonstrate that this particular mica does not bilized, with abundnnt exsolution of needleJike Ti-rich phases. contain any Fe3+,and that Ti is exclusively located on the oc- Analyses of these micas show tetrahedral site with 4.00 or close tahedral sites. to 4.00 atoms, low TiO, (2 to 3o/o)and high AlrO3 (12 to l5Vo) contents, unusual values for lamproitic micas. These crystals are Ti in micas. Various substitution mechanisms have been pro- consideredto be xenocrysts.Other large phlogopites may be found posed to accomodateTi in phlogopite. IfTi is fixed on the oc- 26 WAGNER AND VELDE: K-RICHTERITE-BEARING I-4MPROITES

." o6 "^^+4 "; o5

F 04

rl ra t_ 3s 36 3e 40 "t si*ntf3. Fig.8. ThedistributionofTiandSi + Al + Crinphlogopites from 3 specimens.Solid triangles,74A I ; solid circles,72A7; open # triangles,7B8.

* The incorporation oftitanium on the octahedral site allows for the introduction of a divalent ion, magnesium(Roben, 1981)on (equation positive t.... the tetrahedralsite 4). In this case,a correlation . would exist between Ti and Mg (on the tetrahedral site) and hence a negative correlation between Ti and Si + Al + Cr would ensue. Such a correlation is indeed observed for micas of specimens 7441,7247,11A8, 7B8,8A12, SOl36 (Figs.8, 9 and 10)with Ti contents above 0.26 atoms per structural formula. Among those micas that do show a negative correlation three diferent 76 so groups group (7441, E #ion" can be distinguished:micas from the first 7247 and,7B8) and the second group (8,4.12and I lA8) show Fig.1 . The distribution ofTi and the sum ofcations in phlog- similar slopes of the line defined by the experimental points on opites from 5 specimens.Solid triangles, 74Al; solid circles, Figures 8 and 9, but for a given Ti value the site occupancy by 7247; solid squares,I 1A8; asterisks,7348; open triangles,788. Si + Al * Cr of micas from the first group is higher than the occupancy shown for the second group. This difference is mostly due to a diference in Al content, the micas frorn the first group tahedral site, it replacesa divalent ion, and hence all proposed being richer in Al than micas of the second group. In the third mechanismsare coupled substitutions. These substitutions can type, which only includes specimen50136, mica analysesplot be limited to the octahedral site or involve either one or two along a slope diferent from that defined by the two other groups. other structural sites. The various mechanisms proposed are as follows: Such a substitution schemehowever implies an inverse correlation betweenSi and Ti that is apparentonly in specimen8Al2 2Mg: Ti + D Forbes and Flower (1974) (1) (Fig. I l) and, to a lesserextent, specimen7B8. There is no correlation between the number of Si + Al + Cr 3Mg:1i+Ba+tr Velde(1979) (2) atoms and the Ti content when the number of Ti atoms is below 0.26, indicating a different substitution mechanism. Robert (1976) Mg + 2Si: Ti + 2Al Robert (1976) (3) has proposedsubstitution mechanism(3) when the Ti content is

Mg+Si:Ti+Mg Robert (1976) (4)

Mg + 2OH: Ti + 20 Arima and Edgar(1981) (5) Substitution (l) was proposed after consideration ofthe com- o6 position ofnatural phlogopites, and has been recognized by Velde (1979)for micas found in melilite-bearingrocks where it is prob- o5 ably coupled with a substitution involving the incorporation of barium on the interlayer site. When this mechanism is operative :- 04 a vacancy is created for every 2 Ti atoms entering the structure o3 and the octahedral site occupancy decreases.The existence of {t substitution (l) is demonstratedin Figures 6 and,7 where Ti is o2 *.* I related to the total number of ions. It is of courseassumed that * both the tetrahedral and interlayer sites are filled and that no Fe3* is present in the structure. It appears that for specimens 35 30 37 3A 39 40 586, 8A12, 50136 the slope of the line defined by the experi- Si+Al +C r mental points is close to the expected value, whereas in Figure Fig. 9. The distribution of Ti and the sum Si + Al * Cr in 7 there are more vacancies than would be expected from substi- phlogopitesfrom specimens1 lA8 (solid squares)and 8A 12 (solid tution (l) alone. stars). WAGNERAND VELDE: K-RICHTERITE-BEARING I,,,IMPROITES 27

o5 OO 2'9 'F oo 8'€ o o aa

o o3 orf/ o 28 o2

Si+Al+Cr o.2 03Ti 04 o.s Fig. 10. The distribution of Ti and the sum Si + Al * Cr in Fig. ll. The distribution of Si and Ti in phlogopites from phlogopitesfrom specimen50136 (open circles)and data from specimen8A12, analysesof crystal edges. Mitchell (1981),crosses.

formula, the lowest value found being 0.85. Barium contentsare below 0.35. This substitution was looked for in analysescorre- low, usuallybelow l .006BaO exceptfor specimens7B8 and I 1A8 sponding to the centersof micas from specimensT2A1.and 586 where it reaches 30/0.This low barium content of micas in rocks aswell asfor micasfrom 73,4,8which show low titanium conrenrs. where barium is abundant (see for example data for the Leucite The possibility of this substitution is confirmed by positive cor- Hills volcanics in Carmichael (1967), or as exemplified by the relations between Ti and Al in all three cases. presenceof Ba-rich phasesin some lamproites such as priderite In conclusion it seemsthat the most prominent substitution or barite) is probably due to the alumina-deficiencyofthe bulk mechanisms for Ti in the micas studied are substitutions(l) and composition. Most barium substitutionsinvolve the mechanism (4) for Ti-rich compositions. For Ti contents below 0.26 per Ba + Al : K + Si, an unlikely substitution in peralkaline rocks. structural formula the likely mechanismsare (1) and (3). In the lamproites examined the substitution appears to be of the : Interlayer ions. Ions in the interlayer site (K + Na + Ba) usually kind Ba + n 2K. This vacancy-creating substitution could total close to the theoretical value of 1.0 atom per structural play a role, as does the possible vacancy-creating substitution for Ti. It should be pointed out that micas from specimens7B8 and I lA8 show a correlation between Ti and Ba, with a diferent Table 11. Representativeelectron microprobe analysesofthe slope in each specimen. roedderiteJike phases, from Moon Canyon (analysis l) and Authigenic micas in lamproites differ from phlogopites from Cancarix (analysis 2). For comparison are listed analyses of ultrabasic xenoliths by their high TiO, contents, but xenocrystic roedderite (A, B) and eifelite (C) from Hentschel et al. (1980) micas found in lamproites are similar, even in their trace element and Abraham et al. (1983) respectively contents,with phlogopitesfrom peridotites.

Roedderit e- like p hases Both the Cancarix and the Moon Canyon lamproites contain si02 70.29 69.46 70.60 71.32 69.06 remarkable small prismatic crystals of a pleochroic blue mineral. Alzol o,I7 0.50 o.36 0.57 Electronmicroprobe analysesofthese blue minerals in both spec- FeOo 12.60 9.83 5.80 o.49 0. 19 imens have shown that they have similar compositions to min- Mgo 1I.44 13.90 I 5.70 I7,86 15.47 eralsofthe roedderite+ifelite series(Hentschel et al., 1980;Abra- l'1n0 O.23 o.27 0.21 o.31 0.53 ham et al., 1983).Representative analyses from Cancarix, Moon Tto2 o.o2 o.2t o.o7 o.o7 0.o3 Canyon and ofroedderite and eifelite are reproduced in Table Na2O O.O4 o.25 1.80 5.29 8.O7 I l. The roedderite-like minerals from the lamproites are distinct K2o 4.44 5.14 4.20 4.16 4.16 from those previously described in terrestrial rocks in their com- Total 99.08 99,57 98.88 99,79 98.05 position and in the fact that, for the lamproites, they are part of the mineralogical association, and apparently crystallized from si r2.3to 12.116 12.Loo 11.818 11.92 AI o.035 0,101 0.070 0.08 the liquid. They are closely associatedwith feldspars, amphibole Fez+ 1,845 r.426 0.831 O.068d O.03 and late crystallizing micas. Their chemical compositions are ug 2.947 3.594 4.oI2 4,4I2 3.98 Mn 0.034 o,031 0.o30 o.044 0,08 different from that reported for the Eifel roedderites. The Can- Ti o.oo3 o.o27 0.oo9 o.009 carix mineral (a rare phase in the rock) is a sodium-free and iron- Na O.O14 o. 084 0.598 1.699 2.10 K 1.OO1 1,137 0.918 o.879 0.92 rich relative to the Eifel specimens. The Moon Canyon mineral (quite abundant in the specimen studied) is slightly lessiron-rich,

FeOo: Total iron as FeO more magnesian and sodic than that from Cancarix. The lam- o:Fe3+ proite minerals show a deficit in alkali metals for an R2+ total close to the theorical 5.0 value. Their general formula could be

1, Cancarlx i 2, lloon Canyon derived from the roedderiteformula (Na,K)rMgrSi,rOrothrough : A, B : Hentschel et al., 1980: a substitution of the type Fe3+ Fe2+ + Na. According to this

Cr Abraham et al-., 1983. scheme, the entry of Fe3+ in the structure creates one vacant site (an alkali site), the corresponding end-member being 28 WAGNER AND VELDE: K-RICHTERITE-BEARING LAMPROITES

Table 13. Representative electron microprobe analyses of pseudobrookitesfrom various lamproites studied. Fe3+calculated assuming3 cations and 5 oxygens

1 23 7 4L1 73A8 7B8 t1c77

Al2O3 O.O2 o.47 0.30 0.06 Cr2O3 O.82 o.43 0.99 0.o5 Feoo 28.97 19.66 19.86 23.46 ugo 8.65 9.39 8.92 1.67 MnO O.33 O.15 O.It+ 0.20 z Tio2 60.33 69.O2 69.04 66.32

Total 99.L2 99.72 99.25 97.70

F.2O3 26.38 8.57 7.7t 11.03 FeO 5.24 Lr.94 t2.92 13.54

A1 0.oo1 0.020 0.o13 0,oo3 Cr O,O23 o.012 0.028 0.o01 Fe3+ O.7I4 o.232 0.209 0.307 Fe2+ O.157 o.359 0.390 0.479 Mg 0.464 o.504 0.480 0.420 ltn O.O1O o.oo5 0.oo4 0.006 Ti 1.631 1.868 1.875 L.a44

A4^^^, FeOo : Total lron as FeO

o 2 ,J", Fig. 12. The distribution of Na and Fe2+in roedderite-like plot along the horizontal axis, as they only show a 2Na : Mg phases.Solid triangles,MC77; small solid squares,74,4'1; solid substitution. squares,eifelites (Abraham et al., I 983); solid circles,roedderites The deepblue color ofthe roedderiteJike phaseappears to be (Hentschelet al., 1980). related to the presenceofferric iron in the structure. The Cancarix mineral, richer in iron (total iron) than the Moon Canyon one, KFe3+Fe2+Mg:SirrO3o.This substitution has been proposed by has a deeper blue color. Hentschel et al. and Abraham et al. Hentschelet al. (1980)and Abraham et al. (1983) for roedderites pointed out that their roedderitesC and D, with 5.8 and 4.45Vo found in the Bellerberg volcanic field of the Eifel in Germany. total FeO show a blue color. The Cancarix and Moon Canyon specimens are close to this Roedderite appears among the low-pressure breakdown prod- theoretical end-member. ucts of richterite (Gilbert et al., I 982) and testifiesto the strongly Theserelationships are demonstratedin Figure 12 which rep- peralkaline character of these two lamproites. resentsthe variation of the Fe vs. Na. Na is absent,totally re- placedby Fe3+,in the Cancarix specimen.The iron-free eifelites Oxides Titanium-rich oxides are a general feature of lamproites, as Table 12. Representative electron microprobe analyses of pointed out by Scott Smith and Skinner (1984). In this respect, priderites from Australian, Sisco and Smoky Butte lamproites lamproites differ from peralkaline siliceous rocks that are known for the absenceof oxides (Carmichael, I 967). Besideschromites 12 3 56 1 found as inclusions in olivine (considered below) these rocks so136 SO136 7B8 788 788 8At2 8At2 contain one type of Fe-Ti oxide: ilmenite (1 lA8), or an association oftwo oxides: ilmenite + pseudobrookite (MC77 and 7348); Fe203o 10.97 9. 19 9.53 9.O9 7.66 10.75 9.59 ilmenite + titanomagnetite(586); ilmenite + priderite (50136, l,!Co o.92 O.74 1.15 1.O2 o.76 0. 17 o.03 Sisco); pseudobrookite + priderite (7B8). These minerals and Ti02 76.17 72.89 70.43 68.18 66.60 7t.46 70.83 mineral associations are uncommon and will be described in Cr2o3 0.O3 4.36 0.83 1.85 5.16 o.26 some detail. K20 6.42 1.15 2.56 2.73 2.67 2,27 r.37 Prideritehasbeen found and analyzed (Table I 2) in rocks from Bao 5.43 6.30 16,22 t6.73 16.93 76.39 17.08 Sisco,and Smoky Butte besidesthe Australian type locality. The original priderite contained 0.32 atoms of Ba and 0.87 atoms of Total 1O0.34 1O0,63 99.77 98.69 99.01 99.96 99.16 potassium. Carmichael (1967) gave two electron mieroprobe Fe3+ O.98o o.83O 0.901 0.877 o,141 1.013 o.922 analyses of priderites from the kucite Hills and Australia. The Mg 0.163 0.132 o.2r5 0.195 0.146 0.032 0.oo6 Ti 6,198 6.580 6.653 6.573 6,442 6.132 6.804 priderites from Smoky Butte (where priderite is present in Type Cr O.oO3 0.413 o.o82 0.187 o.525 o,026 I lamproite, as noted by Velde (1975) but has also been found K 1.032 1,095 o.410 0.446 o.438 0.363 o.223 Ba 0.252 0.296 o.798 0.840 o.853 0.803 o.853 in specimen 7B8) are particularly Ba-rich, and the Ba content Total 9.227 9.346 9.060 9.118 9,744 8.943 8.834 canreach0.85 atoms,whereasKis only0.4 per structuralformula calculatedon 16 oxygens.These high Ba-values imply, as hy-

Fe2O3o = Tocal iron as Fe2O3 pothesizedbyPost et al. (1982),the existenceof a Ba end-member ofthe priderite series.Another striking variation in the analyzed WAGNER AND VELDE: K-RICHTERITE.BEARING LAMPROITES 29

I lmenite is accompaniedby priderite in specimen SO I 36 where priderite forms abundant srnall elongated crystals, as well as in some of the Siscospecimens (Velde, 1968)where it is quite rare. Ilmenite forms small crystals (5 to 50 pm maximum) without evidenceofexsolution or oxidation, except for specimen74A1. ol Ilmenites appear after olivine, diopside and the centers of the phlogopites crystals. They are usually poor in hematite, contain- !r ing from 64 to 9090ofthe ilmenite component, I I to 3090geikelite I o't I and I to 290 pyrophanite. Representative analyses are listed in o 6 Table 14.' Specimen 73,{8 conrains probable xenocrysts of a with core; the composition of the maglesian ilmenite a rutile 1l ilmenite is similar, though not as Mg-rich, to that of xenocrystic ,l Mg-ilmenites described by McMahon and Haggerty (1984), a composition closeto the composition of ilmenites found in kim- 6.8 7.2 8.o 8.4 T,* * berlites (Dawson, 1980). Chromites(Table 3) found as inclusions in authigenic olivines Fig. 13. ThedistributionofBa + CrandTi + Kinpriderites. are similar by their high Cr,Or, low AlrOr, and high Mg/(Mg + Solid circles:7B8; solid stars:8Al2; solid triangles:SOl36; solid Fe) to chromites found by Danchin and Boyd (1976) in harz- square:LH9, Carmichael(1967). burgites,themselves, as pointed out by theseauthors, not unlike chromites found as inclusions in diamonds. Their low Al is in priderites is their Cr-content: the priderites found in the Austra- keeping with the peralkaline chemistry of the magma, their high lian specimen may contain 4.36oh CrrOr, the minimum found Cr could be related to the low Al and Fe3+contents ofthe liquid. being0.03. The CrrO, content ofthe Smoky Butte priderite reach- Ti-rich oxides are commonly abundant in peralkaline lam- es 5.16%. The general formula of priderite (Norrish, l95l), proites. This presence and abundance could be ascribed to the A2-yB8-,Or6,is not adequatelyknown, but it seemsthat the vari- high TiO, and high FeO contentsof theserocks. When projected ations observed in the three lamproites mentioned are compatible in an FeO-FerO3-TiO, diagram the composition of most pseu- with a substitution of the type: dobrookite (+ ilmenite) bearing samples plot close to the fer- cr3+ + Ba2+: Ti4+ + K+ (Fig. 13) ropseudobrookite-pseudobrookite line or do so when the amount of iron (and TiOr) partitioned in the early-crystallized silicates This schemedoes not howeveraccount for the observedvariation is taken into account. in the iron content, which could be at least partly in the ferric Most ofthe oxides do not show any exsolution or oxidation state and consequently participate in the above equation. textures and most compositions can be recalculated into ferrous, The presenceand abundance of pseudobrookite, atare mineral rather than ferric, end-members, or minerals with high ferrous in terrestrial rocks, is peculiarly common to some of the lam- iron contents.This observation is taken as an indication of the proites studied. Pseudobrookite usually forms euhedral plates, low oxygencontents of the melts, compatible with the low Fe3+/ hexagonal in shape, opaque or barely translucent in transmitted Fe2+ratio ofmost ferromagnesian silicate phasespresent in these light. When translucent (as in Smoky Butte) crystals can appear lavas. either green or purple brown a difference that does not appear to Oxides are known to occur with phlogopite and richterite in be simply relatedto compositionalvariations. In specimenMC77 ultrabasic nodules, rutile and ilmenite being common, pseudo- pseudobrookite appears as transparent golden brown crystals, brookite rare. with optical properties very close to those ofrutile. In reflected light, these pseudobrookite crystals show reddish internal reflec- Conclusion to the mineralogical description tions. The composition of these oxides is 400/oferropseudo- brookite, 12 to I5o/opseudobrookite and 42 to 480/okarrooite. Lamproites described above can be considered as Representativeanalyses are listed in Table 13. Specimen73,4,8 presenting a magmatic assemblage consisting of Al-poor, contains pseudobrookite crystals, interpreted which as xenocrysts Cr-rich spinel, Ni-rich olivine, Ti-phlogopite, Ti-rich are extremely rich in magnesium (up to 52 moleo/oofthe karrooite K-richterite, diopside, Fe-rich feldspar and Ti-rich oxides. component). This particular pseudobrookiteis close in compo- Olivine crystals having evident textural (kink-bands) anal- sition to armalcolite (Anderson et al., 1970; Haggerty, 1973;El peridotitic found Goresy and Bernhardt, 1974). Pseudobrookitehas been found, ogies with olivines are also and can be as a primary mineral, in few terrestrial rocks: in meteorite im- interpreted as being inherited from the solid layers ofthe pactites (El Goresy dnd Chao, 1976), in kimberlites (Haggerty, earth through which the lamproitic magma percolated. 1975;Raber and Haggerty,1979), in ultrabasicnodules (Cameron Other such inherited minerals are Cr-rich diopsides, Fe- and Cameron, 1973) and lamproites (Velde, 1975). It has also rich clinopyroxenes, Cr-rich phlogopites, pseudobrook- been found in some basalts (Anderson and Wright, 1972; Yan ites, Mg-ilmenites and large rutile crystals (accidental in Kooten, 1980;Von Knorring and Cox, l96l), and in meteorites some Spanish lamproites). Jones and Smith (1983) have (Fujimaki (1971) et al., 1981).It was describedby tuce et al. as also demonstrated the presence, in the Navajo minettes, a quenchedmineral in a dike rock of basaltic composition. Ac- of apatite and clinopyroxenes xenocrysts. The possible cording to Haggerty (1976), the presenceof primary pseudo- presence ofvarious xenocrystic species in the Leucite Hills brookite implies a fast cooling rate that prevents a reaction of Kuehner et al. (1981) who, the pseudobrookite with the liquid, a reaction whose end product lavas was also discussed by would normally be ilmenite. It should be pointed out that in no for example, described pleonaste in the Deer Butte wyo- lamproite was any ilmenite rim found around the early-formed mingite. pseudobrookite. Hence care should be exercised before discussing either 30 WAGNER AND VELDE: K-RICHTERITE-BEARING 1../IMPROITES

o .9 o" E a aa6 : E') 39 .)2 = o + Y o o \o, *? z o * 1 lr *?,a lo o a^^ "."4: ' ' FezFe+Mgamphibole ' 4 1N"ri1o amphibo3te Fig. 16. Partitioningof Fe and Mg betweenphlogopites and richterites.Data from lamproites:solid circles;data from ultra- Fig. 14. The distributionofNa/K calculatedfrom the bulk mafic nodules(A okt, 19 7 4, I 975 andDawson and Smith, I 97 7): rock compositionand the Na,rK content of the A site of the ; solid stars. richterite.Solid circles: data from this study;open circles: data from theliterature: l, LH9, Carmichael(19 67); 2,Type 1,Velde (1975);3, Velde(1978); 4, S84,Bryan (1970); 5, RHl, Barker Na/K ratio. Figure 14 showsthis correlation, as deduced andHodges (1977); 6, Brookset al. (l 978);7, I 2 l, Nichollsand Carmichael(1969); 8, Sheratonand England (1980); 9, S1,Car- from specimensunder consideration and examples taken michael(1967); 10, Jaques et al. 1984. from the literature. Richterites also appear to be more potassicwhen the rock is more peralkaline, which could be anotherway ofexpressingthe previous correlation, the the partitioning of elements between phasesor the sig- peralkalinity in lamproites being directly related to the nificanceof the trace elementgeochemistry of theserocks. potassium content. Partitioning of elementsbetween phases This being established,how are theseelements distributed betweenco-crystallizing phases? Since richterite and Some elementsare found in certain phasesin propor- phlogopite coexist in some ultrabasic nodules brought to tions which can be correlated with the bulk rock com- the surfaceby kimberlitic magma,these nodules represent position. The Fe3+content of the feldspar is simply cor- physical conditions different from those of lamproitic relatedwith the peralkalinity index of enclosingrock. Mi- crystallization, in particular different pressure conditions. cas are more potassium rich in the most potassium rich These data have been included in Figures 16 to 18. In bulk composition, a relation already described by Edg,ar and Arima (1983). Richterites contain variable amounts ofpotassium and there is a relationship between the potassium content of the richterite and the amount of potassium presentin the rock expressedin the form ofthe o6 a 3 o5 o2 o aa oo 6 110 .E E F 64

z2 q* -i8o r_* I a5 o9 o'2 o-4 0'6 , 01 02 03 04 Ti amphibole N"/K retosp.. Fig. I 7 . Partitioning of Ti between micas and richterites. Data Fig. 15. Partitioning of Na and K between richterites and from lamproites: solid circles; data from nodules: solid stars (Aoki, feldspars. Data from this study: solid circles; data from the lit- 1974, 1975; and Dawson and Smith, 1977) and solid squares erature:open circles(a, LH9, Carmichael, 1967;b, Velde, 1978). (data from Joneset al., 1982). WAGNER AND VELDE : K.RICHTERITE. BEARING LAMPROITES 3l

a 10

o a .9 2 Fo4 71 I a o 1 + o3 o l! lr o2 I + ioi z Ba I a 6a

o1 o2 F./F+OH amphibole Si+Almica phlogopites Fig. I 8. Partitioningoffluorine between andrich- Fig. 20. The distribution of (Na + K) - Al calculatedfrom terites.Data from lamproites:solid circles;data from nodules therock bulk compositionsand the Si + Al contentof thephlog- (Jones et al., 1982):solid squares. opites. this way the influence of pressureon the composition of natural mica is 8.50/o(Peterson et al., 1982;Valley et al., the minerals under consideration can be evaluated. 1982) and 4.5o/oin a natural richterite (in a meteorite, Sodium and potassium: there is a direct relationship Olsen et al., 1973). Syntheticminerals contain up to 9.2o/o between the Na/K ratio of richterite and the coexisting F for phlogopites (Kohn and Hatch, 1955) and 4.7o/oin feldspar(Fig. l5). richterite (Kohn and Comeforo, 1955). In lamproite Iron is equally distributed between amphibole and phlogopitesthe fluorine content is, in most cases,below phlogopite (Fig. 16) in lamproites as well as in ultrabasic l0l0,but can reach 40lo(specimen 73,{8). TheseF contents nodules found in kimberlites but this is only valid when are in agreement with what can be calculated from the F consideringthose micas and amphiboles in equilibrium, content of the rock and the modal amount of phlogopite, judged so on the basis of textural arguments(Table l5'). with the exception of specimen I lA8, a rock particularly There is a positive correlation (Fig. 17) between Ti in rich in F-bearing apatite. Representativeanalyses ofF-rich micas and amphiboles. It should be noted that the local- micas and amphibolesfrom lamproites are listed in Table ization of titanium in the amphibole structure is still am- 16.' biguous,and that the problem, for micas, cannot be con- Figure l8 seemsto indicate that F is equally distributed sidered as unambiguously solved even if Ti is probably incorporated on the octahedral site in lamproite micas. Lower Ti-contents appearto characterizemicas and amphiboles from ultrabasic nodules. Fluorine: the maximum content of fluorine found in a

8 2o o a

6 38 E

+ z a

76 7.7 7A ?.9 Si+Al amphibole Si+Al amPhibole Fig. 21. The distribution of (Na + K) - Al calculated from Fig. 19. The distribution of Si + Al in phlogopites and rich- the rock bulk compositions and the Si + Al content of the richterites. terites. 32 WAGNER AND VELDE: K.RICHTERIT:E-BEARING LAMPROITES

Ba./Ba+Na+ K

o02

o q

o ool

9 a a al z a

ooa mtca Fig. 23. The distribution of Bal(Ba * Na t K) in feldspar 3e6 3ea and coexistingmica. l',*o, ,",01i". Fig.22. The distributionof (Na + K) - Al calculatedfrom the rock bulk compositionsand the Si + Al contentof the co- tween feldspar and mica in the lamproites is regular as existingfeldspars. shown on Figure 23. Data from Wiirner et al. (1983) indicate that BaO contentsin phlogopitesare twice the BaO contents in associatedsanidines. Three specimensshow (K" : l) betweenthe two phasesphlogopite and richterite Ko's for Ba betweenfeldspar and mica that are quite com- (Table l5). It should be pointed out that the diagram parable:0. 196 (788), 0.192 (74Al) and 0. I 75 (7247) but includesvalues for specimen73A8 in which the two phas- low when compared to values found in other types of es are not consideredto be in equilibrium (textural evi- volcanic rocks. dence);their F values follow the same trend as that de- Most elements are regularly partitioned between co- termined for phasesthought to be in equilibrium. This existing amphiboles and phlogopites. The bulk compo- observation could be interpreted as indicating that F and sition (either iron, magnesium or titanium contents) exerts OH can equilibrate after crystallization of the two phases. some control on the correspondingcontents of the min- The K" values calculated using the F determinations pub- erals in these elements.The silica saturation is however lished by Joneset al. ( I 982) for mica and amphibole pairs not an important factor in the control of the mineral com- in metasomatized peridotites are widely different from positions, whereasaluminum saturation, on the contrary, one another and from those given here. This anomaly is a determinant factor particularly on the content of the cannot be explained at present.Note should be made of tetrahedral site. the fact that, in the Spanishlamproites, phlogopitesshow a distinct correlation between F and Ti. This correlation Temperatureestimations of cooling history was found in richterites only from specimens74Al,73AB A number of experimental studies have been made on and 7B8. either phlogopites, richterites or oxides. These data can Si + Al on the tetrahedral sites: most of the phases tentatively be used to estimate temperature of crystalli- presentin the peralkaline lamproites do not contain enough zation. Si + Al to fill the tetrahedral site to its theoretical number Initially a spinel+livine geothermometer(Sack, 1982) ofions. This point was discussedin the precedingsection can be used. The authigenic rim around olivine xenocrysts and, in all cases,the nature ofthe other ion (ions) could from the Calasparralamproite give 1000'C (7247) where- not be decided upon with the data at hand. as the olivines from the rock give 800'C. The selagite In spite of the unknown nature of the supplementary spinel-olivine associationsgive values between 914 and ion (or ions) on the tetrahedralsite it is interestingto note 1160.C, whereas a 1000'C phenocryst temperature has that the amplitude of this Si + Al deficiencyis similar in beencalculated for the jumillite (l lA8). In this specimen the coexisting minerals within a given specimen. Figure an olivine coexisting with glass inside an apatite crystal 19 shows the relationship between the value of Si + Al gavea high crystallization temperatureof l22lt with the in the micas and in the coexisting amphibole. There is a method outlined by Watson (1979). positive correlation betweenthe tetrahedral Si + Al con- The maximum thermal stability of the lamproite am- tent ofboth phases.Because tetrahedral deficiency appears phibolesis between985 and 1030"C(Charles, 197 5,1977) to be linked to the peralkalinity of the liquid, the Si + Al taking into account only the Mg-Fe substitution. Richter- content of various phaseshas been plotted against the ite is more stablewhen it is more magnesianand Barton (Na + K) - Al value of the correspondingbulk compo- and Hamilton (1978) have shown that a richterite from sition (Figs. 20 to 22). The apparent correlation is not the Leucite Hills was stableup to 1075"Cat HrO pressures valid for the Jumilla specimen,already commented upon. of I kbar. A crystallization temperature,based upon the Barium is preferentially incorporated in micas (Higuchi partitioning of Na and K betweenamphibole and liquid, and Nagasawa, 1969; Wdrner et al., 1983) but is also has been calculatedfor two specimens(Smoky Butte and presentin coexistingfeldspars. The distribution of Ba be- Jumilla) where amphibole and coexisting glasscomposi- WAGNER AND VELDE: K-RICHTERITE-BEARING I,.IIMPROITES tions were known, using the relation establishedby Helz stituent of some of the nodules found in kimberlites and (1979): the values found are 965'C for Smoky Butte and both minerals have been found as inclusions in diamonds 770'C for Jumilla. (Meyer and McCallum, 1984). Phlogopite-bearingnod- Attempts to estimate temperatureof crystallization us- ules are more frequent than nodules carrying both phlog- ing the oxide phaseswere obviously hindered by the ab- opite and richterite. Thesephlogopites (Dawson and Smith, senceof magnetite and by possible secondaryoxidation. 1977;Aoki, 1974,1975) contain lessTi than the phlog- However one sample (specimen5B6) contains coexisting opites found in lamproites (lessthan 0.I atoms per struc- ilmenite and titanomagnetite which show neither oxi- tural formula), but they also show a tetrahedral site in- dation nor exsolution. These oxides have appearedearly completely filled by Si + Al. in the crystallization sequence,judgrng from textural re- The influence of titanium on the stability of micas is lationships, after clinopyroxene. While titanomagnetite not precisely known. Forbes and Flower (1974) envi- appearshomogeneous, there is a variation in the FerO, sioned that Ti stabilized the phlogopite; Robert (1981) of the ilmenites which decreasesfrom the center towards and Robert and Chapuis (1982) have consideredTi-rich the rims of the crystals. Using a program published by micas as high-pressurephases and this hypothesisis also Ghiorso and Carmichael (1981), two setsof temperatures acceptedby Bachinski and Simpson (1984) who consider were obtained: for the centers of the ilmenites and the the Ti-rich (2.0 to ll.3olo TiOr) cores of minette pheno- magnetitesthe calculatedtemperature is 827.C for a log cryststo have crystallizedat elevatedsubcrustal pressures. .fo, : - 13.5 whereasconsidering the edgesof the ilmenites However, Edgar et al. (1976) establishedthat between I 0 the calculatedcrystallization temperatureis 755"C for log and 30 kbar Ti-poor phlogopite is stable relative to Ti- for: - 15. These resultsare similar to those deduced rich phlogopite. Wendlandt and Eggler (1980) have fur- from the phasediagrams published by Haggerty (1976). thermore shown that the Ti content of the phlogopite Thesetemperature estimations for various minerals or decreasedwith pressure for identical compositions, a mineral pairs allows one to establishthe following: proposition confirmed by Arima and Edgar (1981). All (1) Xenocrysts with included spinels were not found. lamproite micasconsidered in the presentstudy, excepting Olivine xenocryst rims crystallized,at temperatures of xenocrysts,have crystallizedat low pressuresbeing found 1000-1200.c. in rocks that have solidified at the surface.Consequently, (2) Groundmass olivine crystallized at 800-900"C. Ti-rich phlogopitesand amphibolescrystallize under pres- (3) Amphiboles formed at temperaturesbetween 960 surescorresponding to the surface of the earth. The ab- and770"C. senceof Ti-rich phlogopitesin kimberlite nodules, in as- (4) When ilmenite and magnetite are present (Shiprock) semblagesthat, for the most part, include Ti-oxides could temperaturesbetween 800-700rc are indicated. be interpreted as meaning that Ti-phlogopite is not stable These values pertaining to a range oflavas with differing at high pressure. compositions are in broad agreementwith the liquidus determinationsof Carmichael(1967) who found 1165" Discussionand conclusions and 1200'C for two different wyomingites. The data pub- K-Ti-richterites and Ti-phlogopites are the prominent lished by Barton and Hamilton (1978) also for wyoming- minerals found in peralkalinelamproites. They common- ites, in water-saturatedconditions, are in general agree- ly coexist with Tirich Fe-Ti oxides and may be accom- ment with the crystallization order found here. panied by rare alkali-rich phasessuch as priderite, or roed- deritelike minerals. These associations testifu to the High pressurrlow pressurephases. A comparison should peralkaline composition of the liquids from which these now be made with mineral composition recorded from minerals precipitated.Coexistent with, but geneticallyun- ultrabasicinclusions. Common characteristicsbetween ri- related to this magmatic association,are found a number chterites found in nodules and richterites found in lam- ofphasesthat have beenscavenged by the ascendinglam- proites are the following: their potassium content is sim- proitic magma.These phases are the samespecies as those ilar, as is Na/K, their tetrahedralsite is incompletely filled precipitating from the lamproitic magma, i.e., olivine, by Si and Al atoms, but Fe3+is presentin amounts great clinopyroxene, trioctahedral mica, ilmenite, pseudo- enough to saturate the tetrahedral site. These richterites brookite, rutile and apatite. The rate of dissolution being can be distinguished from those found in lamproites by governedby the minerals stableon or closeto the liquidus a lower TiO, content (lessthan 0. I Ti atoms per structural (Brearley and Scarfe, 1984). The volumetric importance formula). Kushiro and Erlank (1970) have obtained re- of these relics is not considerable (less than 100/o)but, crystallization at ll00'C and water pressureof 30 kbar taking into account experirnents performed by Scarfe et of a potassicrichterite close in composition to the Aus- al. (1980) on basalts,material might have been dissolved tralian richterite used as starting material, except for TiO, into the liquid. Incorporation of Ni-rich olivines at depth content: the TiO, content of the starting material was 30/0, could, for example, account for the precipitation of Ni- whereasthe artificial richterite contained only 0.50/oTiOr. rich olivines from the magmaat the surface;incorporation This result implies that the entry oftitanium in the richter- of Cr-rich phasesfor the precipitation of Cr-diopside or ite structue is favored by low pressure. Cr-rich spinels. Phlogopite, as well as richterite, is an important con- Results of the present study show that peralkalinity of 34 WAGNE R AN D VELDE : K- RI CHTE RI TE. BE ARI NG LAM PRO ITE S lamproites is a characteristicof the lamproitic liquid, be- 700/o(weight), but most cluster between 56 and 680/0.Re- causeof the correlations between some mineral compo- quired percentages ofrichterite vary between 30 and 500/0, sitions and the alkalinity index, or the precipitation of Al- except for Jumilla, whose bulk composition has been al- poor chromite as a liquidus phase.Hence contamination tered and will not be considered further, Shiprock and the during the ascent of the magma cannot account for the Australian lamproite. In these two last samples, diopside high alkali (potassium)and low Al contents. must be included in the starting material. In all calcula- Partitioning of elementsbetween phases, excluding xe- tions rutile is added, the proportions being above 10/o nocrysts, is regular and follows trends in keeping with (weight) only for the most titaniferous compositions, those that can be deducedfrom mantle metasomatic as- Smoky Butte and Australia. Recent experiments (Dick- semblagesof phlogopite and richterite. A conclusion is inson and Hess, 1984) have indeed shown that the solu- that the high K-richterites found in mantle xenoliths are bility of rutile (K*) increases dramatically with the KrO/ probably derived from the reactions of highly potassic KrO + AlrO, of the liquids, from 9.5 wt.o/o(K* :0.37) fluids with ultrabasic rocks. The difference between Ti to 41.2 wt.o/o(K* : 0.90). contents of phlogopite and richterite in lamproites (low For the calculated values to match the observed lam- pressure)and metasomatizedperidotites (high pressure) proite compositions, fractionation of olivine, and clino- reflectsthe higher solubility ofTi in these phasesat low pyroxene, and a certain alkali loss must be called for. pressure. The fact that lamproite major elements compositions A deepseated origin ofthese liquids is suggestedby two can be matched in such a fashion cannot be considered seriesof observations: as proofofa particular genetic process. The coincidence The presenceofperidotite xenoliths known to occur in simply permits this scheme to be used as a working hy- the Leucite Hills (Carmichael, 1967; Barton and Bergen, pothesis for a more rigourous treatment of the problem l98l), in the Australian lamproites(Jaques et al., 1984) that would include data on trace elements combined with and in the Spanishlamproites (Velde, 1969; Nixon et al., the precise determination and evaluation of xenocrystic 1982). material that could further constrain the problem. The discovery of diamonds in a number of Australian lamproite localities (Jaqueset al., 1984).This observation Acknowledgments alone placesthe lamproites in a categoryof rocks akin to John Hower gaveDanielle Velde, in 1968,three samplesfrom kimberlites, leastfor at which they originate. at the depth Smoky Butte, Montana; preliminary work on these specimens Trace element data, and in particular rare earth profiles, prornpted a visit to this locality, but large parts of this study when available,indicate for lamproites, asfor kimberlites, ensuedfrom this gift. The first specimenobtained from Moon an extreme enrichment in light rare earth elements(500 Canyon was generouslygiven by M. G. Best, Brigham Young to 2000 the chondritic values),and a weaker enrichment University; the subsequent ones were forwarded to us through in heavyrare earth (Nixon etal., 1982;Mitchell and Haw- the courtesyofProfessor Blanchet,from the University ofBrest. kesworth,1984). The Australian specimen was obtained through Dr. Esquevin, The bulk composition of lamproites is so different from S.N.E.A.P.,Pau. ProfessorA. Baronnet and J. Fabrids reviewed parts preparation, common magmatic rocks that their deviation from, for ofthis manuscript at various stagesofits Pro- fessorW. Schreyer(Jniversity of Bochum) confirmed us in the example, basaltic magmas is not permitted. As pointed opinion that our "roedderite" was probable a new mineral, and (1967) when considering the genesis out by Carmichael Dr. A. El Goresy (Max Planck Institut, Heidelberg) was most of the Leucite Hills volcanics,the temptation is to impose helpful in helping to decipherthe complex relationshipsbetween on the starting material many of the requirements of the opaquephases. result that is supposedto be achieved.Since Carmichael's study, however,the conceptof mantle metasomatismhas References been widely commented upon (Bailey, 1982). Ultrabasic Abraham, K., Gebert, W., Medenbach, O., Schreyer,W., and rocks have beendescribed with a metasomaticassemblage Hentschel,G. (1983) Eifelite, KNarMgSi'rO3s1 I n€w mineral resulting from the reaction of mantle associationswith of the osumilite group with octahedral sodium. Contributions K-rich fluids (Jones et al., 1982:,Barton and Hamilton, to Mineralogy and Petrology, 82,252-258. Anderson, A. T., Bunch, T. E., Cameron, E. N., Haggerty,S. E., precisely 1982) that could be the source ofultrapotassic Boyd, F. R., Finger, L. W., James,O. B., Keil, K., Prinz, M., peralkaline rocks. Ramdohr, P., and El Goresy, A. (1970) Armalcolite: a new It is tempting to pursue this reasoning and calculate mineral from the Apollo I I samples.Proceedings of the Apollo what percentageof the bulk compositions of lamproites I I Lunar ScienceConference, l, 55-63. Anderson, A. T. and Wrieht, T. L. (1972) Phenocrystsand glass with fusion richterite-phlogo- can be explained the ofa inclusionsand their bearingon oxidation and mixing ofbasaltic pite-rutile (or ilmenitepiopside assemblage.kast square magmas, Kilauea Volcano, Hawaii. American Mineralogist, calculations performed using the compositions of these 57, l-188. phasesas listed by Dawson (1980, p. 186) lead to the Aoki, K. (1974) Phlogopitesand potassicrichterites from mica following conclusions:all the bulk compositions of lam- nodules in South African kimberlites. Contributions to Min- eralogyand Petrology, 48, l-7. proites listed in Table 2 can be obtained by the fusion of Aoki, K. (1975) Oriein of phlogopiteand potassicrichterite bear- the above kimberlitic nodule assemblage.In all cases, ing xenoliths from South Africa. Contributiors to Mineralogy required percentagesof phlogopite are between 50 and and Petrology,53, 145-156. WAGNE R AND VELDE : K. RI CH TE RI TE -BEARI NG LAMPRO ITE S 35

Aoki, K., Ishiwaka, K., and Kanisawa, S. (1981) Fluorine geo- ultramafic xenolith survival. (abstr.) Geological Society of chemistry of basaltic rocks from continental and oceanrcre- America Abstracts with Programs, 16, 6. gions and petrogeneticapplications. Contributions to Miner- Brooks, C. K., Noe-Nygaard,A., Rex, D. C., and Ronsbo, J. C. alogyand Petrology,76,53-59. (1978) An occlurenceofultrapotassic dikes in the neighbour- Arima, M. and Edgar, A. D. (1981) Substitution mechanisms hood of Holsteinborg, West Greenland. Bulletin of the Geo- and solubility oftitanium in phlogopitesfrom rocks ofprobable logicalSociety of Denmark, 27,l-8. mantle origin. Contributions to Mineralogy and petrology, 77, Bryan, W. B. (1970) Alkaline and peralkaline rocks of Socorro 288-295. Island,Mexico. CarnegieInstitution of WashingtonYear Book, Armstrong, R. L. (1969) K-Ar dating of the laccolitic centersof 68,194-200. the Colorado Plateauand vicinity. Bulletin ofthe Geological Cameron, K. L. and Cameron, M. (1973) Mineralogy of ultra- Societyof America, 80, 2081-2086. mafic nodulesfrom Knippa quarry, Uvalde, Texas.Geological Bachinski, S. W. and Simpson, E. L. (1984) Ti-phlogopites of Societyof AmericaAbstracts with Programs,5,566. the Shaw's Cove minette: a comparison with micas of other Carmichael,I. S. E. (1967) The mineralogy and petrology of the lamprophyres, potassic rocks, kimberlites. and mantle xeno- volcanicrocks from the L€uciteHills, Wyoming. Contributions liths. American Mineralogist, 69, 4l-56. to Mineralogy and Petrology, 15,24-66. Bailey,D. K. (1982)Mantle metasomatism.Continuinechemical Charles, R. W. (1975) The phase equilibria of richterite and changewithin the earth.Narure, 296,525-530. ferrorichterite. American Mineralogist, 60, 367-3'7 4. Barberi, F. and Innocenti, F. (1967) k rocce selagitichedi Or- Charles,R. W. (1977) The phaseequilibria of intermediate com- ciatico e Montecatini in Val di Cecina. Atti SocietaToscana positions on the pseudobinary NarCaMgrSirOrr(OH)r- ScienzeNaturali, Memorie SerieA, LXXIV. 139-180. NarFerSirOrr(OH)r. American Journal of Science,277, 594- Barbot, J. (1983) Le nickel dans les olivines et les spinellesdes 625. rochesbasiques et ultrabasiques.Thdse 3dme cycle, Universit6 Civetta, L., Orsi, G., and Scandone,P. (1978) Eastwardsmigra- de BretagneOccidentale. tion of the tuscan anatecticmagmatism due to anticlockwise Barker, D. S. and Hodges,F. N. (1977) Mineralogy of intrusions rotation of the appennines.Nature, 276,604406. in the Diablo Plateau,northern Trans-Pecosmagmatic prov- Crittenden, M. D. and Kistler, R. W. (1966) Isotopic dating of ince, Texasand New Mexico. Bulletin of the GeologicalSociety intrusive rocks in the Cottonwood area, Utah. Geological So- of America. 88. 1428-1436. ciety of America SpecialPaper, l0l, 298J99. Barton, M. and Bergen, M. (1981) Green clinopyroxenes and Cross, W. (1897) Igneous rocks of the Leucite Hills and Pilot associatedphases in a potassium rich lava from the Leucite Butte, Wyoming. American Journal of Science,4, ll5-141. Hills, Wyoming. petrology, '77, Contributions to Mineralogy and Danchin, R. V. and Boyd, F. R. (1976) Ultramafic nodules from t0l-tt4. the Premier kimberlite pipe, South Africa. CarnegieInstitution Barton, M. and Hamilton, D. L. (1978) Water-saturatedmelting of WashingtonYear Book 75, 531-538. relations to 5 kbar of three kucite Hills lavas. Contributions Dawson,J. B. (1980) Kimberttes and Their Xenoliths. Minerals to Mineralogy and Petrology,66,41-49. and Rocks. Springer-Verlag,Heidelberg. Barton, M. and Hamilton, D. L. (1982) Water-undersaturated Dawson, J. B. and Smith, J. V. (1977) The venro (mica-am- melting experimentsbearing upon the origin of potassiumrich phibole-rutile-ilmenite-diopside) suite of xenoliths in kim- magmas.Mineralogical Magazine, 45, 267-27 8. berlite. Geochimica et CosrnochimicaActa. 41. 309-323. Bellon, H. (1976) Seriesmagmatiques n6ogdnes et quaternaires Delaney, J. S., Smith, J. V., Carswell,D. A., and Dawson, J. B. du pourtour de la M€diterranee occidentale,compar6es dans (1980) Chemistry of micas from kimberlites and xenoliths- leur cadre gdochronom€trique-Implications dynamrques. II. Primary- and secondary-texturedmicas from peridotites Th0seDoctorat d'Etat, Universit6 Paris-Sud. xenoliths. Geochimica et Cosmochimica Acta, 44,857-872. Bellon, H. (1981) Chronologie radiom€trique (K-Ar) des mani- Dickinson, J. E. and Hess, P. C. (1984) Rutile solubility and festationsmagmatiques autour de la M6diterran6eoccidentale titanium coordination in silicate melts. In M. Brearley, Ed., entre 33 M.A. et I M.A. ProceedingsInternational Conference, Experimental Petrology Laboratory Annual Report. Depart- Urbino University, Italy, 34 l-360. ment of Geology, The University of Alberta, Canada. Bellon, H., Bizon, G., Pedro-Calvo,J., Gaudant, J., and Lopez- Edgar, A. D. and Arima, M. (1983) Conditions of phlogopite Martinez, N. (1981) Le volcan du Cerro del Monagrillo (prov- crystallization in ultrapotassic volcanic rocks. Mineralogical ince de Murcie): 6ge radiomEtrique et corr€lations avec les Maeazine,47, ll-19. s6dimentsn6ogdnes du basin de Hellin (Espagne).Acad6mie Edgar, A. D., Green, D. H., and Hibberson, W. C. (1976) Ex- des Sciences,Paris, Comptes Rendus, s€rie D, 292,11,1035- perimental petrology of a highly potassic magma. Journal of 1038. Petrology, 17, 339-356. Berger,E. T. (198l) Enclavesultramafiques, m6gacristaux et leurs Eissen,J. P. (1982) P6trologiecompar6e de basaltesde diff6rents basaltes-h6tesen contexte oc€anique(Pacifique Sud) et con- segmentsde zone d'accr6tion ocdaniquesi taux d'accrEtion tinental (Massif Central Frangais).Thdse de Docteur ds Sci- vari6s (Mer Rouge, Atlantique, Pacifique).Thdse 3dme cycle, encesNaturelles, Universit6 Paris-Sud-CentreOrsay, 2 vol- Laboratoire de Min6ralogie et P6trographie,Strasbourg. umes,469 p el 92 p. El Goresy,A. and Bernhardt, H. J. (1974) Taurus-Littraw TiOr- Best,M. G., Henage,L. F., and Adams, J. A. S. (1968)Mica- rich basalts: opaque mineralogy and geochemistry. Proceedings peridotite, wyomingite and associatedpotassic igneous rocks ofthe Lunar ScienceConference. 5. 627. in northeasternUtah. American Mineralogist, 53, 1041-1048. El Goresy, A. and Chao, E. C. T. (1976) Identification and sig- Borley, G. D. (1967) Potash-rich volcanic rocks from southern nificance of armalcolite in the Ries glass. Earth Planetary Sci- Spain. Mineralogical Magazine, 3T, 364-369. encektters, 30, 200. Borsi, S., Ferrara, G., and Tongiorgi, E. (1967) Determinazione Feraud, J., Fornari, M., Geffroy, J., and Lenck, P. (1977) Mi- con il metodo del K/Ar delle eta delle rocce magmatichedelle n6ralisationsars6ni€es et ophiolites: le filon d rdalgaret stibine Toscana.Bolletino delle SocietaGeologica Italiana, 86,403- de Matra et sa place dans le district d Sb--ArHg de la Corse 4to. alpine.Bulletin du BRGM (2),Il, 2,91-112. Boyd, F. R. and Nixon, P. H. (1978) Ultramafic nodules from Forbes, W. C. and Flower, M. F. J. (1974) Phase relations of the Kimberley pipes, South Africa. Geochimica et Cosmo- titan-phlogopite lLrMgTiAlrSiuO,o(OH)r: a refractory phase chimica Acta. 42. 1367-1382. in the upper mantle? Earth and Planetary ScienceIrtters, 17, Brearley,M. and Scarfe,C. M. (1984)Dissolution of upper mantle 339-3s6. minerals in alkali-basalt melt at 30 k bar: implications for Fujimaki, H., Matsu-Ura, M., Aoki, K., and Sunagawa,I. (1981) 36 WAGNE R AND VELDE : K- RI CH TE RI TE -B E ARING LAMPRO ITE S

Ferropseudobrookite-silica material-albite-

Peck,L. C. (1964) Systematicanalyses of silicates.U.S. Geolog- Simkin, T. and Smith, J. v. (1970) Minor-element distribution ical Survey Bulletin, I I 70. in olivine. Journal ofGeology, 78,304-325. Peterson,E. U., Essene,E. J., Peacor,D. R., and Valley, J. W. Smith, J. V. (1974) FeldsparMinerals (2). Springer-Verlag,Ber- ( 1982)Fluorine end member micas and amphiboles.American lin. Mineralogist, 67, 538-544. Stefanini, G. (1934) Il complessoeruttivo di Orciatico e Mon- Post,J. E.,Von Dreele,R. B., andBuseck,P. R. (1982)Symmetry tecatini in provincia di Pisa. Atti Societa Toscana ScienzeNa- and cation displacementsin hollandites: structurerefinements turali, Memorie, 44, 224-300. of hollandite, cryptomelane and priderite. Acra Crystallogra- Tateyama, H., Shimoda, S., and Sudo, T. (1974) The crystal phica,B 38 (4), 1056-1065. structure of the synthetic MgIV mica. Zeitschrift fiir Kristal- Prider, R. T. (1982)A glassylamproite from the West Kimberley lographie, 139, 196-206. area,Western Australia. MineralogicalMagazine, 45, 279-282. Valley, J. W., Peterson,E. U., Essene,E. J., and Bowman, J. R. Raber, E. and Haggerty, S. E. (1979) Zircon oxide reactions in (1982)Fluorphlogopite and fluortremolite in Adirondack mar- diamond bearing kimberlites. In F. R. Boyd and H. D. A. bles and calculatedC, O, H, F fluid compositions. American Meyer, Eds., Kimberlites, Diatremes and Diamonds: Their Mineralogist, 67, 545-557. Geology,Petrology and Geochemistry,p. 299-240. American Van Kooten, G. K. (1980) Mineralogy, petrology and geochem- GeophysicalUnion, Washington, D.C. istry of an ultrapotassic basaltic suite, Central Sierra Nevada, Reid, A. M., Donaldson, C. H., Brown, R. W., Ridley, W. I., and California, U.S.A. Journal of Petrology, 21, 651-684. Dawson,J. B. (1975)Mineral chemistry of peridotite xenoliths Velde, D. (1967) Sur un lamprophyre hyperalcalinpotassique: la for the Lashaine volcano, Tanzania. Physics and Chemistry of minette de Sisco (Corse). Bulletin de la Soci6t6 Frangaise de the Earth, 9,525-543. Min6ralogie et de Cristallographie,XC, 214-223. Rice, J. M., Dickey, J. S., and Lyons, J. B. (1971) Skeletalcrys- Velde, D. (1968) A new occrurenceof priderite. Mineralogical tallization ofpseudobrookite.American Mineralogist, 56, I 58- Magazine,36,867-870. t62. Velde, D. (1969) Minettes et kersantites. Une contribution d Robert, J. L. (1976) Titanium solubility in synthetic phlogopite l'6tude des lamprophlres. Thdse de Doctorat d'Etat, Facult6 solid solution. Chemical Geology, 17, 213-227. des Sciences,Paris. Robert, J. L. (1981) Etudes cristallochimiques sur les micas et Velde, D. ( I 975) Armalcolite-Ti-phlogopite-diopside-analcite les amphiboles.Applications d la p€trographieet i la g6ochim- bearinglamproites from Smoky Butte, Garfield County, Mon- ie. Thdsede Doctorat d'Etat, Universit6 de Paris-Sud,Orsay. tana. American Mineralogist, 60, 566-573. Robert, J. L. and Chapuis, G. (1982) Crystal chemistry of Ti- Velde, D. (l 978) An aenigmatite-richterite-olivine trachyte from rich micas: presenceofMgIV and petrological consequences. Puu Koae, West Maui, Hawaii. American Mineralogist, 63, I 3th GeneralMeeting, International MineralogicalAssociation 77t-778. 82, Varna, Bulgaria. Velde, D. (1979) Trioctahedral mica in melilite-bearingeruptive Rock, N. M. S. (1984) Nature and origin of calc-alkaline lam- rocks.Carnegie Institution of WashingtonYear Book, 78, 468- prophyres: minettes, vogesites,kersantites and spessartites. 475. Transactions of the Royal Society of Edinburgh: Earth Sci- Velde, D. and Yoder, H. S. (1983) Partitioning of iron and mag- ences,74, 193-227. nesium betweenmelilite, olivine, and clinopyroxenein lavas. Roden, M. F. (1981) Origin of coexistingminette and ultramafic CarnegieInstitution of Washington Year Book, 82, 256-264. breccia, Navajo volcanic field. Contributions to Mineralogy Von Knorring, O. V. and Cox, K. G. (1961) Kennedyite, a new and Petrology,7 7, 195-206. mineral of the pseudobrookiteseries. Mineralogical Magazine, Ruiz, J. L. and Badiola, E. R. (1980)Laregion volcanica neogena 32,676-682. del surestede Espana.Estudios Geologicos,36, 5-63. Wade, A. and Prider, R. T. (1939) The leucite-bearingrocks of Sack,R. (1982) Spinelsas petrogeneticindicators: activity-com- the West Kimberley area, Western Australia. Quarterly Joumal position relationsat low pressure.Contributions to Mineralogy ofthe GeologicalSociety (London), 96, 39-98. and Petrology, 79, 169-186. Watson, E. B. (1979) Calcium content of forsterite coexisting San Miguel de la Camara, M., Almela, A., and Fuster, J. M. vdth silicate liquid in the system Na2G{aGMgGAl,O3-SiO,. (1952) Sobre un volcan de veritas recientementedescubierto American Mineralogist, 64, 824-829. en el Mioceno de Barqueros(Murcia). EstudiosGeologicos, 7, Wendlandt, R. F. and Eggler,D. H. (1980) The origin of potassic 4tt-429. magmas: l-Melting relations in the systems KAlSiOo- Scarfe,C. M., Takahashie,E., and Yoder, H. S. (1980) Rates of MgrSiOo-SiO, and KAlSiOo-MgO-SiOr-CO, to 30 kbar. dissolution of upper mantle minerals in an alkali-olivine basalt American Journal of Science,280, 385-420. melt at high pressures.Carnegie Institution of Washington Year Williams, H. (1936) Pliocene volcanoes of the Navajo-Hopi Book 79, 29o-296. country. Bulletin of the Geological Society of America, 47, Scott, B. H. (1981) Kimberlite and lamproite dikes from Hol- ttt-t72. steinborg,West Greenland. GeoscienceJournal, 4,3-23. Wbrner, G., Beusen, J.-M., Duchateau, N., Gijbels, R., and Scott Smith, B. H. and Skinner,E. M. W. (1984) Diamondiferous Schmincke,H.-U. (1983) Trace element abundancesand min- lamproites. Journal of Geology, 92, 433-438. eraVmelt distribution coeftcients in phonottes from the Iaacher Seifert, F. and Schreyer,W. (1971) Synthesis and stability of Seevolcano (Germany). Contributions to Mineralogy and Pe- micas in the systemKrO-MgO-SiOr-HrO and their relations trology,84,152-173. to phlogopite.Contributions to Mineralogy and Petrology,30, t96-215. Sheraton,J. W. and England,R. N. (1980) Highly potassicmafic dikes from Antarctica. Journal of the Geological Society of Manuscript received,March 27, 1984; Australia, 27, 129-135. acceptedfor publication, September3, 1985.